Topic 4: Pressure

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Topic 4 Pressure
Pressure, Pascal's Law, and Hydraulic Systems
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Pressure ForceArea

• p F/A
• The unit for pressure is the pascal, which is
  written as Pa.
• 1 Pascal 1 Newton/1 square meter
• Pa N/m2
• Eg. A woman has a weight of 600 N, and the soles
  of her feet have a combined area of 0.5 m2, what
  is the pressure on her feet?
• p F/A 600N/0.5m2 1200 Pa.

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Pascals Law

• In a closed system, where the fluid cannot
  escape, any pressure that is placed on the fluid
  will be transmitted equally in all directions.
• Pascals law is used in hydraulic systems like
  car lifts.
• Hydraulic systems involve a large mechanical
  advantage.

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Hydraulic Systems

• Hydraulic systems involve a small cylinder which
  pressurizes the liquid. Pascals law says that
  the pressure will travel, undiminished,
  throughout the liquid.
• In a hydraulic system the pressure will cause the
  cylinder at the other end to raise up.

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Pascals Law and Hydraulics

• According to Pascals law, the pressure is the
  same on both ends, therefore the force at the
  larger cylinder (larger area) will be larger than
  the effort force going onto the smaller cylinder.
• pressurein pressureout?Fin/Ain Fout/Aout

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Example

• A mechanic exerts a force of 200 N on a 0.5 m2
  piston cylinder. At the other the large, 10 m2
  cylinder moves up. What is the most force that it
  can exert upward?
• pinput Finput/Ainput 200 N/0.5 m2 400 Pa
• pinput poutput 400 Pa
• Foutput 400 Pa X 10 m2 4000 N